Impact of Rituximab in the Clinical Outcomes of Hairy Cell Leukemia: A Retrospective Single-Institution Analysis

Background: Hairy cell leukemia (HCL) is an indolent mature B-cell disorder that comprises ~2% of all leukemias. Purine nucleoside analogues (PNA) such as cladribine and pentostatin remain the standard initial treatment with high response rate, however frequent late relapses occur. The addition of rituximab (R) has shown efficacy as a single agent and in combination in the first- and second-line settings . Recent data suggests that the addition of R to PNA increased the minimal residual disease (MRD) negative (neg) and duration of response (DOR) when compared to PNA alone. In this study, we examined the impact of rituximab (R) in the long term outcomes of HCL from a single institution experience.

Methods: An IRB-approved retrospective analysis was performed including patients with HCL or HCL-variant who were seen at Moffitt Cancer Center between 1/2000 and 2/ 2019. Primary endpoints were overall (OS) and progression-free survival (PFS). Secondary endpoints included overall response rate (ORR). Complete Remission (CR) was determined based off of accepted criteria of Hgb > 11gr/dL, platelets > 100,000/µL and ANC > 1500/µL. Statistical comparisons and survival analyses were performed using SPSS^TM Statistics and GraphPad Prism^TM.

Results: We identified 124 cases with available treatment data and follow up (82 HCL, 15 CD25-negative HCLv). The median follow-up was 72 months. The median age was 57 years (27 - 89+). The 5 and 10 year OS was 97% and 91%, respectively, with 2 deaths reported secondary to HCL or complications from HCL. The median PFS for all patients receiving first-line therapy was 92 months. Clinical risk factors present at diagnosis that were independently associated with worse PFS after first-line therapy were weight loss (HR 2.27, p = 0.057), recurrent infections (HR 2.50, p=0.009) and splenomegaly (HR 1.87, p=0.047),, hemoglobin less than 11 gr/dL (HR 3.12, p=0.016), and negative CD25 (HR 2.14, p=0.055). In multivariate analyses, negative CD25, recurrent infections and Hgb < 11 gr/dL were associated with worse PFS after first line therapy (p = 0.002). Most patients received PNA alone or PNA+R (96 and 18, respectively) as first line with a higher CR rate in the PNA+R group (100% vs 71%) and a higher median PFS for [not reached (NR) and 82 months, respectively, p = 0.165] with 2 relapses in the PNA+R group (both at 30 months). In the 2^nd line setting, PNA+R (n = 11) was also associated with a higher CR rate than PNA alone (n = 22, 82% vs 64%) with only 1 relapse in the PNA+R group at 97 months. The median PFS for 2^nd line PNA+R vs 2-CdA was 97 and 43 months, respectively (p = 0.253).

Conclusions: In this study, we report a large, retrospective, single-institution dataset of HCL and HCLv patients with long-term follow-up. The addition of R may improve the PFS in patients with HCL in the first and 2^nd -line settings however a longer follow up is needed. A recently described prospective randomized trial in the use of concomitant rituximab plus PNA has reported a higher MRD free CR in comparison with PNA alone but not PFS yet.